Quantikel-Theorie der chemischen Bindung

Abstract

A. The quanticule theory bases the representation of the electronic structure of substances on physical principles which permit correlation of precise experimental data and yet are sufficiently simple for elementary teaching. In the present chemical literature the following concepts are widely used for a similar purpose.

For typical carbon compounds:

1. Classical single, double and triple valence bonds (V.B.), e.g., H–C≡C–Cl Main idea: mutual saturation of a definite number of forces emerging from neutral atoms.
2. Complete stable electron groups, mainly octets (O.), resulting for each element from sharing electron pairs (P.) between neighboring atoms, each pair forming a single covalent bond, e.g., H:C:::C:Cl:.

For typical salt-like compounds:

1. Electrostatic attraction between oppositely charged rigid ions, preferably of stable noble-gas type structure.

B. The customary approach encounters varions difficulties which nowadays are reflected in the application to a growing number of substances of multiple “mesomeric” or “resonance” forms. It is shown in the present article that the main reasons leading to this complexity are :

a) Contrary to the postulate mentioned in 2, shared electrons cannot complete stable electron configurations for each of two bonded atoms.

b) It is inconsistent to use for molecule ions, side by side, classical bonds which are supposed to indicate saturation, and electric charges which can be more or less effectively screened but not saturated.

c) The properties of innumerable substances do not correspond to the concepts 1—3, but could be thought to be intermediate between the properties expected for two or more hypothetical structures compatible with 1-3.

C. Quanticule formulations are based on the following two general principles.

I. The electrons within molecules and crystals can be subdivided, as in atoms, into groups (quanticules) quantized with respect to definite nuclei or cores. The quanticules can consist of various numbers of electrons and be quantized with respect to variuns numbers of nuclei or cores.

II. The decrease of potential energy accompanying all types of chemical binding is almost completely due to electrostatic forces of attraction and repulsion acting within and between the quanticules and the respective cores, with a negligibly small contribution of magnetic forces.

D. The relation between the concepts 1-3 and the principles I and II ist as follows. The shared electron pair constitutes according to 1 and 2 the covalent bond, A:B. According to I and II, this type of binding is appropriately expressed by A⁺(e^-)₂B⁺; the quanticule (e^-)₂, quantized with respect to the two cores A⁺ and B⁺, represents just one of variois types of molecular quantization. When B⁺ = A⁺ the bond is nonpolar, i. e., the degree of polarity, p, equals zero.

In the case of the binding A⁺B^-, there are two quanticules, each quantized with respect to a single nucleus either of A or of B. Neglecting the electronic polarizability of A⁺ and B^-, one has the ideal ionic binding of rigid ions with p = 1.

Substances with degrees of polarity between 0 and 1 are represented according to c) as hybrids of fractional covalent and ionic character. On the other hand, the quanticule theory assigns a unique quantization to every molecular species. Here the different values of p are due, as has been realized for a long time, to the following physical phenomena : in the case of ionic quantization to the mutual continuous polarization (deformation) of the ions A⁺ and B^-; in the case of the quantization A⁺(e^-)₂B⁺ to a continuous shift of the charge of (e^-)₂ towards the stronger field of the cores A⁺ or B⁺.

E. Among the numerous kinds of molecular quanticules, other than (e^-)₂, and their corresponding cores are:

α) Eight-electron quanticule, one core X^m+, with m between 4 and 7, besides one or several H+, e. g., H₃N = (3 H⁺, N⁵⁺)(e^-)₈.

β) Eight-electron quanticule, cores B³⁺ in

B₄C_l4 = (B₄)⁴⁺(Cl^-)⁴ = [(e^-)₈4B³⁺]4Cl^-.

γ) Ten-electron quanticule, two of the cores C⁴⁺, N⁵⁺ or O⁶⁺, e.g., C₂^2- = C⁴⁺(10e^-)C⁴⁺ or CO = C⁴⁺(10e^-)O⁶⁺.

δ) Six-electron quanticule, characteristic of aromatic character, quantized with respect to five, six or seven cores C⁴⁺ in a homocyclic ring, e.g., C₆H₆ = (e^-)₆[C⁴⁺(e^-)₂]₆,6H^-.

F. The quanticule theory bases the interpretation of modern precise data on appropriately selected electron configurations and electric interactions between cores and electrons, without using empirical additive increments for atoms, ions or bonds. For instance, it is not surprising that in chloroacetylene the internuclear distances (in Å) for the classical C–H or C–Cl bonds are not equal to those in chloromethane, since the kinds of quantization and the directions of polarity involved are different: H⁺_1.052(CC)^2-_1.632Cl⁺ and (H^-_1.11)₃C⁴⁺_1.732Cl^- respectively.